0102: Instruction Register Emulation & PCB Design | 16-Bit Computer From Scratch 

@yashindane2844 -- That is a great question! I made some mistakes with my choices, so let me help you not make the same mistakes. It's a long response. I made lots of mistakes! There are a few considerations when making that decision, which I did not think all the way through. One important thing to keep in mind is that LS logic is unable to drive HC logic high levels. What do I mean by that? LS logic can output a high value that is as low as 2v4 (read that as "2.4v" if you are not familiar with the notation) and still properly register that as high whereas HC logic accepts as high signal no lower than 3v5 (I think I have the exact voltages wrong, but go with me here). Important side note: The exact voltages are in the datasheet and you should get used to reading them. They are a slow read and important details will be buried in odd locations, so I recommend reading them for content and reading every word. That is a big task for some devices. The point here is that there is a difference between the high output of LS and the high input of HC and this difference will need to be corrected somehow. If it is not corrected, then you will get some odd errors while you are building your system out. They are difficult to track down. So, the answer is simple, then: don't mix them. I thought the same thing as well and then chose LS for the breadboard build and HC for the PCB build. And then I started to hook the 2 builds together for testing. You did not mention PCBs but I assume you will get there at some point as maintaining a breadboard in a working state is a big job as well and you will end up wanting something a little more permanent. It was in mixing the 2 builds for testing I realized I had a problem I had not considered -- the majority of my build over time was going to be in a mixed state. I was using incompatible logic. There are ways around it, but it is messy and you are testing in a state which is not the final configuration. You can mix LS and HC logic by using the HCT family instead of the HC family. HCT are HC logic but *TTL Compatible* (read: they can be driven by LS level inputs). Another thing to consider is: What you are going to connect as interfaces and what logic-levels do they use? That may force you into using HCT for anything that directly connects to that device. It is also likely you might need to level-shift the voltages (putting 5v into a 3v3 input will cook the device, guaranteed; 3v3 is not quite enough to drive a 3v5 input). LS is going to have a higher power draw than HC. So you might consider that based on the number of ICs you will require. Fan-out is also a concern. LS can only drive about 10 or so other transistors directly whereas I have read that HC can drive as many as 5000 gates directly (again, my numbers are probably not exact and you need to check the datasheet for each IC). Switching speed (or clock frequency) is also a concern. Some parts of your circuit may be forced into "A" family logic, where the "A" is "Advanced". These switch faster than the other typical LS and HC logic, but there is an increased cost/IC. These can be mixed easy enough with same logic type (AHC with HC) as long as the outputs of the AHC are slow enough to meet the requirements of the HC inputs. Finally, if you are using 16-bit computer as your entry point into digital electronics, I would encourage you to take a few smaller steps first. If you have not already, take a look at Ben Eater (ru-vid.com/group/PLowKtXNTBypGqImE405J2565dvjafglHU&si=Dg3z1Hduamzq8zjn) and James Sharman (ru-vid.com/group/PLFhc0MFC8MiCDOh3cGFji3qQfXziB9yOw&si=y2y5-VZ0JLyFpgLd). Both have 8-bit builds (the respective playlists are linked), each with different architectures. You see, I'm really no expert and I'm not convinced mine is working 100% yet. I doubt I have all the underlying issues sorted out and I know theirs work. Good luck and please share updates on your build!

@@eryjus4594 thanks Sir, for taking time to respond with so many details! I have a doubt, can we say HCT can act as a Bridge between LS and HC family? Can HCT safely drive HC inputs?

Sorry it took so long to reply. @davehohacks has a great video on this. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-v0XSIeZpeCo.htmlsi=FB-CG_j99CGu8hfm